Using a group of lab
mice, chemicals, electric shocks and light, scientists have
managed to recover previously lost memories.

The process of memory consolidation, when a short-term, unstable
memory turns into a long-term one, takes place in so-called
memory engram cells - a collection of specific neurons. In the
experiment detailed in Friday's report, a group of lab mice were injected
with a virus which made these neurons produce a light-sensitive
protein, thus activating in response to light.

The mice were put in a chamber where they received an electric
shock. The rodents remembered the exerience and came to associate
it with the chamber. When they later were taken into the chamber,
they froze in place.

The mice were then injected with a chemical called anisomycin,
which prevents memory consolidation. After that, the animals no
longer showed signs of recognizing the chamber where they had
been electrocuted before.

Then, the scientists used pulses of light to activate their
engram cells. After that, the animals again started freezing in
fear when brought to the electric shock chamber.

"These findings are probably applicable to certain conditions
of human amnesia, such as an early stage of some Alzheimer's
patients," Susumu Tonegawa, director of the Japanese RIKEN
Brain Science Institute, and one of the authors of the reports,
said.

What this means, researchers say, is that memories that appear to
be lost due to illness and trauma, could actually just be just
blocked, while remaining recoverable.

The exact mechanism of amnesia has not been completely
discovered. While some scientists believe it is caused by
permanent damage to memory-storing neurons, others, like Susumu
Tonegawa, believe it is the blockage of access to those neurons
that is the problem. In the latter case, not all is lost for
human amnesiacs.